Apparatus for lifting flasks and molds

ABSTRACT

Apparatus, including stripping pins and master actuator therefore, is disclosed for the handling of flasks or molds. The stripping pins and actuator are constructed to insure positive and synchronized displacement of all of the stripping pins, regardless of variations in external loads applied to the individual pins. The actuator utilizes an hydraulic circuit and an optional pneumatic-hydraulic circuit to effect actuation of the stripping pins.

llited States Patent Young 1 Dec. 24, 1974 APPARATUS FOR LIFTING FLASKS AND MOLDS [75] Inventor: Lester Charles Young, Cleveland,

Ohio

Assignee: Combustion Engineering, lnc.,

Windsor, Conn.

Filed: Dec. 13, 1972 Appl. No.: 314,892

US. Cl 60/547, 60/565, 60/581, 60/593, 164/44 Int. Cl. FlSb 7/00 Field of Search 60/547, 563, 565, 572, 60/579, 580, 581, 584, 585, 593; 91/411,

References Cited UNITED STATES PATENTS 5/1938 Mclnnerney 60/581 3/1939 Bowen 2/1952 Sparks et a1. 60/580 2,856,222 10/1958 Gossett et al. 91/165 3,040,534 6/1962 Hager 60/563 3,257,810 6/1966 Hanni 60/547 3,643,725 2/1972 Fismer 164/44 FOREIGN PATENTS OR APPLICATIONS 157,750 12/1932 Switzerland 9l/165 Primary Examiner-Martin P. Schwadron Assistant ExaminerA. M. Zupcic Attorney, Agent, or Firm-Stephen A. Schneeberger [57] ABSTRACT 4 Claims, 4 Drawing Figures PATENTEU UE241974 sum 2 M g PRESSURIZED AIR FIG- 1 FIG. 3

APPARATUS FOR LIFTING FLASKS AND MOLDS BACKGROUND OF THE INVENTION The invention relates generally to molding operations and equipment and more particularly to lifting mechanisms for lifting the flask or mold from a support member.

In casting various items, molds are formed by impressing a pattern in the upper and/or lower surface of a quantity of sand peripherally retained within a flask or mold liner. Following the step of impressing the pattern in the sand, the flask and mold must be removed or stripped from the surface on which they are supported, for transport to another station.

The stripping operation must be done with care to insure mold integrity. In one system, described in US. application Ser. No. 131,750 filed on Apr. 6, 1971 for Foundry Mold Making Apparatus, stripping pins are urged into contact with the lower surface of the flask prior to separation of the upper and lower pressure members from the mold, the lower pressure member begins to move downward and the stripping pins upward to a limit position, resulting in a down strip separation of the mold from both the upper and lower pressure members.

This down stripping sequence has the limitation, however, of requiring the finished mold to be held in the compaction region while the stripping pins are being initially actuated. Occasionally it is preferred that the mold be lowered with the lower pressure member and the stripping operation is begun after such lowering begins.

Accordingly, it is advantageous to also have the ability to initiate the stripping operation at a time when the load on the stripping pins is no greater than that of the flask and mold which may be quite light, as in the instance of molds for piston rings. Further, the geometry of the mold may place different loads on each stripping pin, particularly if the pins are more than two in number.

A flask and mold stripping arrangement is required which will lift a flask and/or mold of any weight from a support member, evenly, with no twisting. The several stripping pins are required to move upwardly, relative to a supporting structure, exactly in unison, even under conditions of very light external preload, as with lightweight molds.

SUMMARY OF THE INVENTION The present invention provides a combination of stripping pins and actuating mechanism to be operated with little or no preload by the mold or flask and which results in even stripping or lifting of a mold from a supporting member. The stripping pins are internally biased to a lower limit position and independent hydraulic supply circuits to each pin from a common liquid reservoir are utilized to overcome the bias and move the pins upward in stripping operation. Use of a remote hydraulic drive system provides flexibility in locating the stripping pins.

Each independent circuit includes a branch cylinder with a piston therein, the piston having a fluid passage therethrough communicating with the common reservoir and the respective stripping pin. Each branch piston includes a valve for closing the fluid passage during movement of the piston and means are provided for moving all of the branch pistons in unison. Further, the

branch piston moving means mechanically close the valves prior to the initiation of downward motion of the branch pistons.

The stripping pin biasing force may be provided by an hydraulic circuit interconnecting all of the pins and acting downwardly thereon. Both the biasing and the driving hydraulic circuits may be operated using a pressurized gas, with the former transmitting a pressure to the pins and the latter driving a main actuating piston which moves the branch pistons to displace fluid in the circuits. The liquid reservoir common to all of the branch cylinders is vented to the atmosphere to prevent inadvertent pressurizing of any driving circuit while its associated piston valve is open.

This arrangement insures positive control and uniform synchronized actuation of all of the stripping pins. The liquid reservoir maintains a supply of liquid in the branch cylinders even in the event of some leakage by the stripping pins.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially schematic vertical sectional view of a stripper pin assembly and master actuator therefor, both taken through the centers thereof, the latter along line l--l of FIG. 3.

FIG. 2 is an enlarged view of the poppet valve assembly.

FIG. 3 is a sectional plan view of the master actuator housing taken along line 33 of FIG. 1.

FIG. 4 is a schematic representation of the master actuator, stripping pins and associated fluid circuitry in a complete stripping system.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, there is shown in FIG. 1 a stripping pin assembly 10 typical of at least one other, and preferably three other, similar such assemblies, seen schematically in FIG. 3, as associated with a mold-making apparatus, not shown. A mold, or mold flask 12 is supported in known manner by part of the lower support structure of the mold-making apparatus, for instance on a pattern plate, prior to and during the mold forming operation. Pin assemblies 10a, 10b, etc. are fixedly mounted on the lower support structure at a common elevation beneath the flask 12 for actuation into contact therewith. The pin assemblies 10a, 10b, etc. are laterally positioned to conveniently accommodate flask 12.

A pin assembly 10 comprises a housing 14 having a cylinder 16 and a piston 18 slidably mounted in cylinder l6 and dividing it into upper and lower parts or chambers. A piston rod 20 is integrally formed with piston 18 and extends upwardly therefrom through and in sliding relation with a sealed opening in the top of housing 14. A bottom cover 22 sealingly closes the bottom of cylinder 16 and serves to limit the downward travel of piston 18. A port 24 in housing 14, at or near the bottom of cylinder 16 permits a non-compressible liquid, such as oil, entry into and egress from the cylinder below piston 18. A similar port 26 in housing 14 at or near the top of cylinder 16 permits a fluid, preferably though not necessarily non-compressible, such as oil, entry into and egress from the cylinder above piston 18. A bottom vent drain 28 may be opened to bleed for drain gas or liquid from the lower part of cylinder 16 when the system is not in operation. A similar top vent drain, not shown in FIG. 1, may be opened to bleed or drain gas or liquid from the upper part of cylinder 16 when the system is not in operation. While each pin assembly a, 10b, etc. will include a bottom vent 28, only one of the assemblies will require a top vent, not shown, as will become obvious hereinafter.

Piston 18, and accordingly piston rod 20, are normally biased in the downward direction to a lowered position in contact with bottom cover 22. The bias force might be provided in a variety of ways; however, according to the preferred embodiment of the invention, the bias force is provided by a fluid in the upper part of cylinder 16 acting to displace piston 18 downward. This biasing mechanism will later be described in greater detail. The lowered position of piston 18 and piston rod 20 is represented in the left half of pin assembly 10, as depicted in FIG. 1, wherein the upper end of the piston rod is spaced, slightly below flask 12.

When an actuating force of greater magnitude than the existing downward force is applied upwardly to piston 18, the piston and rod move upward to a raised limit position, as represented in the right side of the pin assembly 10, as depicted in FIG. 1. At a point intermediate the lowered" and raised" positions, piston rod 20 contacts and lifts flask 12 from the support on which it had been resting.

A master actuator is mounted either on the moldmaking apparatus or remote therefrom and is controlled to actuate the piston 18 of each pin assembly 10a, 10b, etc., between the lowered and raised positions. Actuator 30 includes a housing comprised principally of a body member 32 and a cover member 34 thereabove. A domed member such as bowl 36, above the cover 34, may also form part of the housing.

Body member 32, a plan view of which is seen in FIG. 2, comprises a block-like member having, in this embodiment, four piston-housing branch cylinders 38 extending downwardly thereinto about the center from the upper surface. Pistons 40 of circular cross-section are in each of the cylinders 38 in close sliding relationship therewith. Concentric bores 42 in the bottoms of and of smaller diameters than each of the cylinders 38 create lower guide and seating surfaces for springs 44 which extend upwardly therefrom into bores 46 in the underside of pistons 40. Springs 44 are seated against the base of bores 46. Additional bores in member 32 concentric with and of smaller diameter than bores 42, extend from bores 42 through the bottom of member 32 to create ports of passages 48. Each port 48 is adapted to be connected in sealed fluid conveying relationship to an end of a fluid conduit 49a, 49b, etc., the other end of which is connected to the port 24 on corresponding stripping pin assembly 10a, 10b, etc. Each piston 40 includes an annular seal 50 about its circumference to fluidly separate the upper and lower regions of cylinders 38.

The upper end of each piston 40 is of reduced diameter to provide an upwardly facing stop-contacting surface 52 at the shoulder. A bore 54 in the reduced diameter upper portion of the piston provides a guideway for a poppet valve 56 with a smaller concentric bore 58 providing a guideway and lower seat for poppet valve spring 60. A further bore extends between bores 58 and 46 and is concentric therewith and of lesser diameter than either, to form passage 62 which allows fluid communication therebetween.

Poppet valve 56 comprises a circular head or holder 64, adapted to slide within bore 54, having a disk 66 of fluid sealing material, such as Teflon, affixed to the undersurface thereof, as by screw 68. Spring 60 is seated at one end on the bottom face of bore 58 and extends upwardly about the head of screw 68 into yielding supportive engagement with the underside of disk 66. The bore 58 in each piston 40 is of smaller diameter than disk 66 which is concentric therewith. The upwardly facing land created by bore 54 provides a valve seat surface 70 for sealing disk 66. Spring 60 is of such design that disk 66 is biased upwardly and normally spaced from valve seat 70. Further, a spring 60 is designed to yield to significantly less force than is required to cause yielding of a branch cylinder spring 44. Several radially extending passages 63 extend through the reduced diameter portion of each piston 40 to communicate with the bore 54 at its bottom to permit liquid communication between chamber 76 and the lower portions of cylinders 38.

Cover member 34 includes a flanged base portion open in the center and of the same general peripheral cross-sectional geometry as the peripheral upper surface of body member 32 for mating engagement therewith about their respective perimeters. A fluid sealing gasket 72 is interposed between the mating surfaces of body 32 and cover 34 and screws 74 act to maintain the body and cover in fluid-tight engagement with one another.

Cover 34 further includes a large vertically extending hollow cylindrical portion extending upwardly from the base portion and being essentially closed at its upper end and open at its lower end in registry with the open center of the cover member base portion to form a large cylindrical chamber 76 in fluid communication with the upper ends of every one of the branch cylinders 38 and pistons 40. Chamber 76 serves both as a central reservoir for the liquid, such as oil 78, which is controllably introduced to or exhausted from the lower region of stripping pin cylinders 16, and also as a piston housing. A closable fill hole 79 extends through cover 34 to chamber 76 to allow filling and emptying of the chamber.

The diameter of chamber 76 is such, particularly at its lower end, that the base flange of cover member 34 extends inwardly somewhat over part of each branch cylinder 38, and accordingly, over part of the major diameter of each piston 40 therein. This inwardly extending part of cover 34 defines a stop 80 which limits the upward travel of pistons 40 when contacted by their stop contacting surfaces 52.

A main actuating piston 82, of generally domed shape with a skirt depending from a thick circular upper end portion, is within chamber or main cylinder 76 in close vertical sliding relationship with the walls thereof. Piston 82 has an upwardly extending boss at its top center with contacts the roof or upper wall of reservoir 76 to limit upward travel of the piston and maintain a small air space 83 thereabove. An annular seal 84 about the circumference of piston 82 serves to prevent liquid and impede gas passage thereby. Annular recesses in piston 82 below seal 84 collect any gas which passes the seal and several small vent holes 86 extend radially through the piston wall from the recesses to convey the gas to an air space 88 within the interior of the piston and chamber 76.

Each poppet valve holder 64 is sized and spring biased such that it extends above the uppermost surface of piston 40 a somewhat greater distance than disk 66 is above valve seat 70. At least part of the base of the skirt of piston 82 is vertically aligned with at least part of holder 64 and is preferably in contact therewith in its upper limit position. Piston 82 may be moved from its upper limit position downwardly in contact with holder 64 to close poppet valve 56 as will be explained. The base of the skirt of piston 82 is preferably a continuous ring and the piston will reach an absolute lower limit of travel when the piston base contacts the upper face of body member 32, as between the several branch cylinders 38.

Piston 82 is biased to its upper limit position by a spring 90 acting in compression between the underside of the piston and the body member 32. Spring 90 is coaxially disposed about a vertically extending tube 92 seated in the upper part of body member 32 at or near the center thereof. Tube 92 is vertically in registry with a narrow bore extending vertically through body member 32 to form vent 94, which provides fluid communication between chamber 76 and the atmosphere. Tube 92 determines the maximum depth of oil 78 in chamber 76, assuming it remains open to the atmosphere.

One or more holes or ports 96 extends through cover 34 at an elevation such that it communicates directly with air space 83 above piston 82 in its upper limit position. Port 96 is adapted for connection to a controllable source of driving fluid, such as pressurized air supply 98, as seen in FIG. 4. A control valve 100 in conduit 102 intermediate air supply 98 and port 96 allows air to be controllably introduced to or vented from air space 83 above piston 82. Bowl 36 is a hollow dome shaped member, closed at its upper end, preferably transparent, which is sealingly mounted, as by screws 103 to the top of cover member 34 to create a chamber 104 therebetween. Three separate passages or ports 106, 108 and 1 extend through an upper solid portion of cover member 34 between the atmosphere and chamber 104. Port 106 may be closed and serves as a fill hole by which oil 112 may be introduced to or emptied from chamber 104.

A tube 114, open at both ends, extends vertically from cover member 34 to near the top of bowl 36 therewithin and is in sealed fluid conveying relationship with port 108. Port 108, like port 96, is adapted to be connected, through an air conduit 1 l6 and vented con trol valve 118, to air supply 98.

Port 110 is adapted to be connected in sealed fluid conveying relationship with an end of conduit 120a which is connected at its other end to port 26 on stripping pin assembly 10a, with the ports 26 on the remaining assemblies 10b, 10c, etc. being interconnected therewith by conduits 120b, 120e, etc., as seen in FIG. 4.

Further, as seen in FIG. 4, fill ports 106 and 79 are adapted to be connected to one another and to a source of oil, not shown, by conduit 122. A control valve 124 controllably isolates both chambers 76 and 104 from the oil source and a control valve 126 may be used to isolate chamber 76 from 104. Control valve 126 may be opened from time to time to increase the oil level in one chamber and decrease that in the other, as might be needed due to leakage of oil past stripping pin pistons 18.

Operation of the stripping pins and the master actuator therefor will now be considered. Hydraulic fluid, such as oil, is admitted to chambers 76 and 104 through open valves 124 and 126 in conduit 122 which is connected to an oil source. Bottom vents 28 and a single top vent, not shown, are opened in the stripping pin assemblies 10a, 10b, 10c, etc. to vent air and to allow oil to completely fill the cylinders 16 on both sides of pistons 18, the conduits 49a, 49b, etc. and 120a, 120b, etc., branch cylinders 38 and the reservoir portions of both chambers 76 and 104. Bowl 36 is filled to a level somewhat above the halfway point on tube 114 in chamber 104 and chamber 76 is filled to the level at which oil begins to vent to the atmosphere through tube 92 and vent 94, these levels generally appearing in the left side of actuator 30 depicted in FIG. 1. Piston rods 20 may be pushed or loaded to their downward limit position to aid the filling. Valves 124 and 126 are then closed to isolate the two chambers, or reservoirs.

Control valve 118 is opened to admit air under a pressure of about 20 PSI to the upper region of bowl 36, thereby pressurizing the oil 112 therein and creating the downward biasing force on each stripping pin piston 18, as mentioned earlier. This pressurization and biasing force is preferably continuously maintained; however, it might be interrupted during upward actuation of pistons 18 if so desired.

To actuate pistons 18 upward, control valve 100 is opened to admit air to the air space 83 over piston 82. This air is at sufficient pressure relative to the crosssectional area of piston 82 to provide a force thereon which is sufficient to overcome the biasing forces of spring 90, springs 60, springs 44 and the downward bias, if any, on stripping pin pistons 18. This bias on pistons 18 may include one internally applied and/or the load of a flask and mold.

As pressurized air is introduced to air space 83, piston 82 begins to move downwardly, depressing poppet holders 64 and disks 66 relative to pistons 40. Disks 66 will become seated against valve seats to sealingly isolate oil in cylinders 38 and beyond, from that in chamber 76. Continued downward movement of piston 82 is transmitted through poppet valve 56 to pistons 40 which in turn begin to move downward in unison. Pin pistons 18 move upward in response to the oil displaced from branch cylinders 38. The strip pin pistons 18 each are sized relative to one another and branch pistons 40 are each sized relative to one another in cross-sectional area, such that equal axial displacement of pistons 40 results in equal axial displacement of pistons 18 The branch pistons and cylinders are sized relative to the strip pin pistons and cylinders such that pistons 18 reach their upper limit positions, seen in right half of FIG. 1, somewhat before pistons 40 reach their bottom limit. The bottom limit for pistons 40 is reached when the base portion of master piston 82 contacts the upper surface of body 32, as seen in the right half of actuator 30 in FIG. 1. When the stripping pin pistons 18 and rods 20 are in the raised" position, position, flask or mold 12 supported thereon may be removed therefrom.

As stripping pistons 18 are driven to their upper limit, oil is displaced from cylinders 16, raising the level of oil 112 in bowl 36, as seen in the right half of actuator 30 in FIG. 1. The initial filling of bowl 36 should be such as to keep this latter mentioned level somewhat below the top of air tube 114.

During downward actuation of piston 82, the volume of air space 88 is reduced. Such reduction initially occurs before poppet valve 56 is closed and if chamber 76 were not vented to the atmosphere, the resulting pressure would be transmitted through the hydraulic system to the undersides of pistons 18. If the downward forces on pistons 18 varied, as is possible, the pistons might react in a non-uniform, and thus undesirable, manner. However, vent 94 serves as an air bleed which maintains the air in space 88 at atmospheric pressure, thus avoiding the mentioned problem.

To return the stripping pin pistons to their initial lower limit position, valve 100 is operated to disconnect port 96 and air space 83 from air supply 100 and vent them to the atmosphere. The pneumatic pressure maintained (or, possibly, re-established) on oil 112 drives the pistons 18 downward. As oil is driven from the bottom of cylinders 16 and air is exhausted from air space 83, piston 82 and branch pistons 40 move upward to their initial, or non-actuated, positions seen in the left half of actuator 30 in FIG. 1. Poppet valves 56 open to re-establish fluid communication with oil 78 in chamber 76. Any slight oil leakage past pistons 18 during the cycle is made up from this reservoir.

As pistons 18 return to their initial lower limit position, the level of oil 112 in bowl 36 returns to the lower level seen in the left half of actuator 30 in FIG. 1. If oil from chamber 76 leaks past any strip pin piston 18, it will accumulate in bowl 36. This oil may, from time to time, be returned to chamber 76 by opening valve 126 and closing it when oil begins to overflow through vent 94.

The above-described operating cycle will be repeated each time a mold and flask 12 are to be lifted or otherwise spaced from a supporting member. Valves 100 and 118 may be such that they controllably vent or exhaust air to the atmosphere from air space 83 at a rate which controls the rate of descent of pistons 18 and rate of ascent of pistons 40 and 82. Actuator 30 is preferably positioned at a higher elevation than the pin assemblies a, 10b, etc., so that any air bubbles in the hydraulic systems will find their way to the vented air spaces in the actuator.

The several oil fill ports and pressurized air ports shown in the upper portion of cover 34 may, of course, be located at different positions about the circumference of the cover than those shown herein.

It will be understood that the embodiment shown and described herein is merely illustrative and that changes may be made without departing from the scope of the invention as claimed.

What is claimed is:

1. Apparatus for lifting a mold relative to a support member, comprising in combination:

a. plural lifting means each including a lift cylinder stationary relative to said support member and a lift piston movable therein for actuation between lowered and raised positions for lifting said mold when actuated to said raised position;

b. means biasing each of said lift piston to said lowered position; and

means for actuating said lift pistons in unison to said raised position comprising:

i. a liquid reservoir,

ii. plural branch cylinders each in liquid communication with a different one of said plural lift cylinders below said lift piston in its lowered position,

iii. piston means in each said branch cylinder having a liquid passageway extending therethrough and selectively in liquid communication with said reservoir,

iv. means biasing each said branch piston to a reference position remote from the lift cylinder communicating end of said branch cylinder;

v. normally open poppet valve means with each said branch piston for selectively closing said passage therethrough, and

vi. selectively actuable pressure responsive means for actuating said poppet valve means to the closed state and for moving said branch pistons only in unison toward the lift cylinder communicating end of said branch cylinder.

2. The apparatus of claim 1 wherein said valve closing and branch piston moving means comprise a main actuating piston actuable into simultaneous closing engagement with said poppet valve means and simultaneous driving engagement with all of said branch pistons and normally biased out of said driving engagement therewith.

3. Apparatus for lifting a mold relative to a support member, comprising in combination:

a. plural lifting means each including a lift cylinder stationary relative to said support member and a lift piston movable therein for actuation between lowered and raised positions for lifting said mold when actuated to said raised position;

b. means biasing each of said lift piston to said lowered position; and

0. means for actuating said lift pistons in unison to said raised position comprising:

i. a housing;

ii. a liquid reservoir in said housing including an air space therewithin;

iii. plural branch cylinders in said housing, each in liquid communication at one end with said reservoir and at the other end with a different one of said plural lift cylinders below said lift piston in its lowered position,

iv. piston means in each said branch cylinder having a liquid passageway extending therethrough,

v. means biasing each said branch pistons toward said reservoir communicating end of said branch cylinder,

vi. a main atuating piston in fluid communication with said reservoir and selectively fluidly actuable into simultaneous driving engagement with all said branch pistons for moving said branch pistons only in unison toward the lift cylinder communicating end of said branch cylinder and normally biased out of said driving engagement therewith,

vii. normally open valve means for each said branch piston for closing said liquid passageway therethrough during all movement of said branch piston toward the lift cylinder communicating end of said branch cylinder, whereby liquid displaced from each said branch cylinder by said moving branch piston overcome said lift piston biased to proportionally displace each respective lift piston, and

viii. an air vent tube extending between said air space within said reservoir and the atmosphere, whereby liquid in said reservoir is maintained substantially at atmospheric pressure during actuation of said main actuating piston.

4. Apparatus for lifting a mold relative to a support member, comprising in combination:

a. plural lifting means each including a lift cylinder stationary relative to said support member and a lift piston movable therein for actuation between lowered and raised positions foir lifting said mold when actuated to said raised position;

b. means biasing each of said lift pistons to said lowered position comprising:

i. a first liquid reservoir,

ii. fluid conduit means connecting said first reservoir with said lift cylinders above said lift pistons in their raised positions,

iii. a source of pressurized gas, and

iv. means for applying said pressurized gas to said first reservoir to pressurize liquid therein; and

0. means for actuating said lift pistons in unison to said raised position comprising:

i. a housing,

ii. a second liquid reservoir in said housing,

iii. plural branch cylinders in said housing, each in liquid communication at one end with said secent one of said plural lift cylinders below said lift piston in its lowered position,

iv. piston means in each said branch cylinder having a liquid passageway extending therethrough,

v. means biasing each said branch piston toward said reservoir communicating end of said branch cylinder,

vi. a main cylinder in said housing,

vii. a main actuating piston slidably movable within said main cylinder and actuable into simultaneous driving engagement with all of said branch pistons for moving said branch pistons only in unison toward the cylinder communicating end of said branch cylinder,

viii. means for selectively applying said pressurized gas to said main cylinder to control actuation of said main actuating piston, and

ix. normally open valve means with each said branch piston for closing said liquid passageway therethrough during all movement of said branch piston toward the lift cylinder communicating end of said branch cylinder, whereby liquid displaced from each said branch cylinder by said moving branch piston overcomes said lift piston bias to proportionally displace each respective said lift piston. 

1. Apparatus for lifting a mold relative to a support member, comprising in combination: a. plural lifting means each including a lift cylinder stationary relative to said support member and a lift piston movable therein for actuation between lowered and raised positions for lifting said mold when actuated to said raised position; b. means biasing each of said lift piston to said lowered position; and means for actuating said lift pistons in unison to said raised position comprising: i. a liquid reservoir, ii. plural branch cylinders each in liquid communication with a different one of said plural lift cylinders below said lift piston in its lowered position, iii. piston means in each said branch cylinder having a liquid passageway extending therethrough and selectively in liquid communication with said reservoir, iv. means biasing each said branch piston to a reference position remote from the lift cylinder communicating end of said branch cylinder; v. normally open poppet valve means with each said branch piston for selectively closing said passage therethrough, and vi. selectively actuable pressure responsive means for actuating said poppet valve means to the closed state and for moving said branch pistons only in unison toward the lift cylinder communicating end of said branch cylinder.
 2. The apparatus of claim 1 wherein said valve closing and branch piston moving means comprise a main actuating piston actuable into simultaneous closing engagement with said poppet valve means and simultaneous driving engagement with all of said branch pistons and normally biased out of said driving engagement therewith.
 3. Apparatus for lifting a mold relative to a support member, comprising in combination: a. plural lifting means each including a lift cylinder stationary relative to said support member and a lift piston movable therein for actuation between lowered and raised positions for lifting said mold when actuated to said raised position; b. means biasing each of said lift piston to said lowered position; and c. means for actuating said lift pistons in unison to said raised position comprising: i. a housing; ii. a liquid reservoir in said housing including an air space therewithin; iii. plural branch cylinders in said housing, each in liquid communication at one end with said reservoir and at the other end with a different one of said plural lift cylinders below said lift piston in its lowered position, iv. piston means in each said branch cylinder having a liquid passageway extending therethrough, v. means biasing each said branch pistons toward said reservoir communicating end of said branch cylinder, vi. a main atuating piston in fluid communication with said reservoir and selectively fluidly actuable into simultaneous driving engagement with all said branch pistons for moving said branch pistons only in unison toward the lift cylinder communicating end of said branch cylinder and normally biased out of said driving engagement therewith, vii. normally open valve means for each said branch piston for closing said liquid passageway therethrough during all movement of said branch piston toward the lift cylinder communicating end of said branch cylinder, whereby liquid displaced from each said branch cylinder by said moving branch piston overcome said lift piston biased to proportionally displace each respective lift piston, and viii. an air vent tube extending between said air space within said reservoir and the atmosphere, whereby liquid in said reservoir is maintained substantially at atmospheric pressure during actuation of said main actuating piston.
 4. Apparatus for lifting a mold relative to a support member, comprising in combination: a. plural lifting means each including a lift cylinder stationary relative to said support member and a lift piston movable therein for actuation between lowered and raised positions foir lifting said mold when actuated to said raised position; b. means biasing each of said lift pistons to said lowered position comprising: i. a first liquid reservoir, ii. fluid conduit means connecting said first reservoir with said lift cylinders above said lift pistons in their raised positions, iii. a source of pressurized gas, and iv. means for applying said pressurized gas to said first reservoir to pressurize liquid therein; and c. means for actuating said lift pistons in unison to said raised position comprising: i. a housing, ii. a second liquid reservoir in said housing, iii. plural branch cylinders in said housing, each in liquid communication at one end with said second reservoir and at the other end with a different one of said plural lift cylinders below said lift piston in its lowered position, iv. piston means in each said branch cylinder having a liquid passageway extending therethrough, v. means biasing each said branch piston toward said reservoir communicating end of said branch cylinder, vi. a main cylinder in said housing, vii. a main actuating piston slidably movable within said main cylinder and actuable into simultaneous driving engagement with all of said branch pistons for moving said branch pistons only in unison toward the cylinder communicating end of said branch cylinder, viii. means for selectively applying said pressurized gas to said main cylinder to control actuation of said main actuating piston, and ix. normally open valve means with each said branch piston for closing said liquid passageway therethrough during all movement of said branch piston toward the lift cylinder communicating end of said branch cylinder, whereby liquid displaced from each said branch cylinder by said moving branch piston overcomes said lift piston bias to proportionally displace each respective said lift piston. 